System and method for utilizing oil and gas wells for geothermal power generation

ABSTRACT

A method and system for extracting geothermal heat from a well is provided, wherein the well casing has positioned therein an inner pipe nested within an outer pipe. The space between the well casing and the outer pipe may be filled with an insulating medium. A liquid heat conducting material flows into and down through the inner pipe. The inner pipe may be fitted with a one-way valve so that the liquid heat conducting material does not reverse direction and flow upwards towards the surface. As the liquid heat conducting material approaches the bottom of the inner pipe, it enters into a heat exchanger, absorbs heat and transforms to its gaseous state. The gas rises upward through the space between the outer pipe and the inner pipe and into the electricity generating component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority based upon prior U.S. Provisional Patent Application Ser. No. 61/994,186 filed May 16, 2014 in the name of Richard L. Wynn, Jr., entitled “SYSTEM AND METHOD FOR UTILIZING OIL AND GAS WELLS FOR GEOTHERMAL POWER GENERATION,” the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of converting geothermal energy into electricity or other forms of work. More specifically, the present invention relates to capturing geothermal heat from deep within a drilled well and bringing this geothermal heat to the earth's surface to generate work, for example in the form of electricity, in an environmentally friendly process.

Wells that have been drilled for oil and gas exploration that are either depleted, or have never produced oil or gas, usually remain abandoned and/or unused and may eventually be filled. Such wells were created at a large cost and create an environmental issue when no longer needed for their initial use.

Wells may also be drilled specifically to produce heat. While there are known geothermal heat/electrical methods and systems for using the geothermal heat/energy from deep within a well (in order to produce a heated fluid (liquid or gas) and generate electricity therefrom), these methods have significant environmental drawbacks and are usually inefficient in oil and gas wells due to the depth of such wells.

More specifically, geothermal heat pump (GHP) systems and enhanced geothermal systems (EGS) are well known systems in the prior art for recovering energy from the earth. In GHP systems, geothermal heat from the earth is used to heat a fluid, such as water, which is then used for heating and cooling. The fluid is actually heated to a point where it is converted into steam in a process called flash steam conversion, which is then used to generate electricity. These systems use existing or man-made water reservoirs to carry the heat from deep wells to the surface. The water used for these systems is extremely harmful to the environment, as it is full of minerals, is caustic, and can pollute water aquifers. Such deep-well implementations require that a brine reservoir exists or that a reservoir is built by injecting huge quantities of water into an injection well, effectively requiring the use of at least two wells. Both methods require that polluted dirty water is brought to the surface. In the case of EGS systems, water injected into a well permeates the earth as it travels over rock and other material under the earth's surface, becoming polluted, caustic, and dangerous.

A water-based system for generating heat from a well presents significant and specific issues. For example, extremely large quantities of water are often injected into a well. This water is heated and flows around the inside of the well to become heated and is then extracted from the well to generate electricity. This water becomes polluted with minerals and other harmful substances, often is very caustic, and causes problems such as seismic instability and disturbance of natural hydrothermal manifestations. Additionally, there is a high potential for pollution of surrounding aquifers. This polluted water causes additional problems, such as depositing minerals and severely scaling pipes.

Geothermal energy is present everywhere beneath the earth's surface. In general, the temperature of the earth increases with increasing depth, from 400°-1800° Fahrenheit at the base of the earth's crust to an estimated temperature of 6300°-8100° Fahrenheit at the center of the earth. However, in order to be useful as a source of energy, it must be accessible to drilled wells. This increases the cost of drilling associated with geothermal systems, and the cost increases with increasing depth.

In a conventional geothermal system, such as, for example, an enhanced geothermal system (EGS), water or a fluid (a liquid or gas), is pumped into a well using a pump and piping system. The water then travels over hot rock to a production well and the hot, dirty water or fluid is transferred to the surface to generate electricity.

As mentioned earlier herein, the fluid (water) may actually be heated to the point where it is converted into gas/steam. The heated fluid or gas/steam then travels to the surface up and out of the well. When it reaches the surface, the heated water and/or the gas/steam is used to power a thermal engine (electric turbine and generator) which converts the thermal energy from the heated water or gas/steam into electricity.

This type of conventional geothermal system is highly inefficient in very deep wells for several of reasons. First, in order to generate a heated fluid required to efficiently operate several thermal engines (electric turbines and generators), the fluid must be heated to degrees of anywhere between 190° Fahrenheit and 1000° Fahrenheit. Therefore the fluid must obtain heat from the surrounding hot rock. As it picks up heat it also picks up minerals, salt, and acidity, causing it to very caustic. In order to reach such desired temperatures in areas that lack a shallow-depth geothermal heat source (i.e. in order to heat the fluid to this desired temperature), the well used must be very deep. In this type of prior art system, the geologies that can be used because of the need for large quantities of water are very limited.

The deeper the well, the more challenging it is to implement a water-based system. Moreover, as the well becomes deeper the gas or fluid must travel further to reach the surface, allowing more heat to dissipate. Therefore, using conventional geothermal electricity-generating systems can be highly inefficient because long lengths between the bottom of a well and the surface results in the loss of heat more quickly. This heat loss impacts the efficacy and economics of generating electricity from these types of systems. Even more water is required in such deep wells, making geothermal electricity-generating systems challenging in deep wells.

Accordingly, prior art geothermal systems include a pump, a piping system buried in the ground, an above ground heat transfer device and tremendous quantities of water that circulates through the earth to pick up heat from the earth's hot rock. The ground is used as a heat source to heat the circulating water. An important factor in determining the feasibility of such a prior art geothermal system is the depth of wellbore, which affects the drilling costs, the cost of the pipe and the size of the pump. If the wellbore has to be drilled to too great a depth, a water-based geothermal system may not be a practical alternative energy source. Furthermore, these water-based systems often fail due to a lack of permeability of hot rock within the earth, as water injected into the well never reaches the production well that retrieves the water.

SUMMARY OF THE INVENTION

The present invention discloses, generally, a system and method of economically conducting geothermal heat from a well to the earth's surface and then using this heat to generate electricity or other forms of work in a closed-loop system. This system and method is environmentally responsible because there is no fluid flow through the ground within the earth. It is entirely based on heat flow from thermal zones or rocks deep within a well through solid materials to heat contents of pipes pumped in a closed loop from and to the earth's surface.

The present invention discloses a system for generating electricity or other forms of work using geothermal heat from within a drilled well, comprising a heat harnessing component having a closed-loop heat extraction system. In various embodiments of the invention, the closed-loop heat extraction system consists of an inner pipe nested within an outer pipe, wherein the inner pipe and outer pipe are configured to create a heat exchange zone which cause a liquid heat conductive material within the inner tube to undergo a phase change to a gas phase. The rock or hot water surrounding the well casing heats the heat conductive material. Because the pressure change resulting from the liquid to gas phase change may cause back pressure on the liquid heat conducting material flowing into the inner pipe, a one-way valve may be installed to prevent backflow. Gas flowing from the heat exchange zone to the surface can be thermodynamically converted from heat to work.

The system may further include insulation between the well casing and the outer pipe. The insulation may be configured to facilitate the flow of heat through the well casing and towards the outer pipe in and around the heat exchange zone, and configured to impede the flow of heat away from the outer pipe in other areas to maintain a temperature of the contents of the piping system substantially constant as the contents of the piping system are pumped to the surface of the well. The closed-loop heat extraction system extracts geothermal heat from the well without exposing the rock surrounding the heat exchanger to a liquid flow.

The foregoing has outlined rather broadly certain aspects of the present invention in order that the detailed description of the invention that follows may better be understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features and wherein:

FIG. 1 is a block view of a system according to one embodiment of the present invention;

FIG. 2A is a horizontal cross-sectional depiction of pipes in a well casing according to one embodiment of the present invention;

FIG. 2B is a vertical cross-sectional depiction of pipes in a well casing according to the same embodiment of the present invention as shown in FIG. 2A;

FIG. 3A is a horizontal cross-sectional depiction of pipes in a well casing according to another embodiment of the present invention;

FIG. 3B is a vertical cross-sectional depiction of pipes in a well casing according to the same embodiment of the present invention as shown in FIG. 3A;

FIG. 3C is a depiction of a perspective view the end of pipes in a well casing according to the same embodiment of the present invention as shown in FIG. 3A;

FIG. 4 is a schematic diagram of a thermodynamic power cycle in accordance with one embodiment of the present invention in which heat-exchange medium is circulated and compressed in a well in a vertical configuration,

FIG. 5 is a schematic diagram of a thermodynamic power cycle in accordance with another embodiment of this invention in which heat-exchange medium is circulated and compressed in a well in a vertical and then horizontal configuration; and

FIG. 6 is a conceptual flow-chart describing the process of oil and gas well reconfiguration for conversion to geothermal electricity power generation.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to improved methods and systems for, among other things, extracting geothermal heat from within a bore hole. The configuration and use of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of contexts other than extracting heat from wells. Accordingly, the specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention. In addition, the following terms shall have the associated meaning when used herein:

“heat exchanger” means any device or apparatus used or useful for the transfer of heat from one medium to another;

“insulation” means any material used or useful in altering the rate of heat transfer; and

“pipe” means any pipe, tube, conduit, channel or other device or apparatus used for conveying fluid.

In the following description of the present invention reference is made to the accompanying drawings which form a part thereof, and in which is shown, by way of illustration, exemplary embodiments illustrating the principles of the present invention and how it may be practiced. It is to be understood that other embodiments may be utilized to practice the present invention and structural and functional changes may be made thereto without departing from the scope of the present invention.

The present invention economically and efficiently conducts geothermal heat from deep within a well to the surface of the earth, and then uses this geothermal heat to generate electricity in a closed-loop system. This closed-loop system generates electricity by heat flow within a closed circulatory system rather than by the conventional water flow, so that it does not require large quantities of water separately injected into the well or pumped from the depth of the well.

Referring to FIG. 1, embodiments of the present invention include a heat harnessing component 101 and a component 102 for converting the heat to work. The heat harnessing component 101 includes a heat exchanging element 104, and a heat conductive material 100 that transfers geothermal heat from hot rock near a bottom 109 of the well 110 to the heat exchanging element 104. Embodiments also includes a piping system 105, comprised of one or more downward-flowing pipes 106 and one or more upward-flowing pipes 108. The piping system's 105 contents, pumped from and to the surface by a pumping mechanism 103, include a heat conductive fluid or gas that flows through the closed-loop system and carries heat to the surface of the well 110. The electricity generating component 102 includes a thermal engine 120 which converts heat into electrical energy. Liquid discharged from the thermal engine 102 may be held in a liquid holding reservoir 111 before being pumped by the pumping mechanism 103. The thermal engine 120 may include an electric turbine and a generator. The piping system 105 thermodynamically couples the heat harnessing component 101 and the electricity generating component 102.

The downward-flowing pipes 106 and the upward-flowing pipes 108 of the piping system 105 may be insulated with insulation known in the art. The diameter of the downward-flowing pipes 106 and the upward-flowing pipes 108 used in the piping system 105 may vary, and should be determined in accordance with the desired flow requirements. In one embodiment, the downward flowing pipes 106 and the upward flowing pipes 108 are integrated into a single element, to the fullest extent possible, in order to simplify installation.

In another embodiment, one or more downward-flowing pipes 60 and one or more upward-flowing insulated pipes 108 are made of a flexible material and can be spooled into the well 110. The piping system 105 is therefore flexible and may be comprised of several different layers of wound corrosion resistant steel wiring. The number of layers used in any one particular pipe in the piping system 105 will be determined as a function of the depth of the well 110 and pressure/temperature requirements.

Utilizing the pumping mechanism 103 and the piping system 105, contents of the piping system 105, which may be a heat conductive fluid comprised of liquid or gas, is piped downward through one or more downward flowing pipes 106 and into the well 110. The downward flowing pipes may be fitted with a one-way valve 112 to prevent the fluid from moving towards the surface. The contents are pumped downward through one or more downward pipes 106 to a level of the well 110 where there is significant geothermal heat that is sufficient to heat the contents. This lowest depth where the first appropriate heat is encountered will be referred to hereinafter as the heat point 130, although it is understood that there is geothermal heat at many levels and this geothermal heat becomes greater as the depth of the well 110 increases. The area between the heat point 130 and the bottom 109 of the well 110 is here called the high-yield thermal zone or just thermal zone.

The heat exchanging element 104 is positioned in the thermal zone at a point between the heat point 130 of the well and the bottom 109 of the well 110. The downward-flowing pipes 106 are coupled to this heat exchanging element 104 on a first side 150, allowing the contents to pass through the heat exchanging element 104 on the first side 150 of the heat exchanging element 104. The heat exchanging element 104 draws geothermal heat from the earth using the heat conducting material 100 which interfaces with the hot rock surrounding the thermal zone and uses this geothermal heat to heat the contents as they pass through the heat exchanging element 104. Unlike conventional systems which will simply draw a heated fluid from a well to the top surface, and then utilize a heating element in order to further heat the fluid at the surface level, the present invention has its heat exchanging element 104 actually contained deep within the well 110 itself. The heat exchanging element 104 and the heat conductive material 100 form a closed-loop, solid state extraction system in which heat flows rather than water. This closed-loop, solid state extraction system has no negative environmental impacts and only requires the presence of hot rock.

The thermal zone is constructed at a desired depth after a surface area of the surrounding rock has been increased to ensure maximum temperature and flow of geothermal heat generated by the rock. A variety of techniques, discussed herein, may be employed to increase surface area of the rock. Increasing the surface area of the rock ensures a steady, continual equilibrium temperature and maximum flow of geothermal heat from the surrounding rock and into the heat conductive material 100, which is injected after the thermal zone is constructed. Therefore, the present invention increases the surface area of the rock surrounding the to-be-built thermal zone as much as possible, as doing so improves heat flow from the rock to the heat conductive material 100 to the heat exchanging element 104 to the contents of the piping system 105.

One method of increasing the surface area of the rock is by fracturing the rock surrounding the thermal zone to create cracks and crevices that expand the surface area. The present invention contemplates that many ways of fracturing the rock may be used, including through hydraulic fracturing (“hydro-fracting”, or “fracking”), through drilling bore holes in multiple directions as described herein, and generally any current or future method of breaking or fracturing rock deep under the earth's surface.

Accordingly, the equilibrium temperature is the temperature, or range of temperatures in one embodiment, in the system and method of the present invention at which geothermal heat heating the contents of the piping system 105 equals the rate at which the hot rock supplying the geothermal heat recoups, or re-generates, the heat it is transferring out. If geothermal heat is transferred out above the equilibrium temperature, geothermal heat in the hot rock will be depleted or dissipated, and rate and temperature of the heat extraction deteriorates. If geothermal heat is transferred out at or below the equilibrium temperature, the rate of heat extraction will be continual and steady, therefore a steady state heat extraction system is achieved.

Heat exchanging elements generally are devices built for efficient heat transfer which typically transfer heat from one working medium to another. For example, some heat exchanging elements feature fluids of two different temperatures flowing along opposing sides of a heat exchanging element, with one fluid heating the other. Heat exchanging elements are well known in the art and are widely used in many engineering processes. Some examples include intercoolers, pre-heaters, boilers and condensers in power plants.

Referring now to FIGS. 2A and 2B, one or more upward-flowing pipes 108 of the piping system 105 are coupled to the heat exchanging element 104 on a second, opposing side 160 of the heat exchanging element 104. One or more upward-flowing pipes 108 draw the heated contents from the heat exchanging element 104 and bring the heated contents upward from the heat point 130 in the well 110 to the surface. The bore hole from the heat point 130 to the top of the well 110 may be completely insulated to prevent heat loss. The heat exchanging element 104 and the piping system 105 form a closed loop that separates the contents from the environment creating a completely environmentally-friendly system.

In one embodiment, the fluid that needs to be heated (or, also used herein, the contents of the piping system 105) may be optimized to carry heat. An example of such a fluid is antifreeze used in automobiles. Gas or water may also be used as a fluid. Further, it may be desirable that the fluid not have any corrosive properties, and that the material used to construct the piping system 105 be resistant to the fluid. Moreover, the fluid may be pressurized within the piping system 105 so the system is able to withstand pressure generated by the depth of the well 110 and the pumping mechanism 103, as the fluid is pumped through the system. The fluid used is environmentally inert and causes no environmental issues should the piping system 105 break.

Referring still to FIGS. 2A and 2B and construction of a system according to embodiments of the present invention, once the piping system 105 and heat exchanging element 104 are fully installed in the well 110, the thermal zone is completely filled with the heat conductive material 100. Once the heat conductive material 100 fills the thermal zone, the rest of the bore hole of the well 110 may be filled with insulation 107. The heat conductive material 110 must be able to retain and conduct heat efficiently, maintaining a substantially constant temperature throughout the thermal zone. The heat conductive material 100 connects the hot rock surrounding the thermal zone to the heat exchanging element 104, creating the heat harnessing component 101.

The heat conductive material 100 used in the present invention may take many forms. Generally, any substance or material that conducts heat at the temperatures required within a well 110 may be used.

Additionally, the present invention contemplates that one or more additional materials 111 may also be injected into a well 110 (via a pipe such as large diameter pipe 112 and may be used to capture and conduct geothermal heat generated from surface area of the rock. Examples of such additional materials 111 include, but are not limited to, ball bearings, beads, wire or metallic mesh, and pipes. Such additional materials 111 increases the conduction of the geothermal heat by filling cracks and crevices in the rock surrounding the thermal zone. By expanding the surface area of the rock surrounding thermal zone and using the additional materials 111, the capacity of the heat conductive material 100 is expanded. The additional materials 111 increase the surface area of conduction, meaning that geothermal heat conducted from the rock surrounding the thermal zone is released over greater surface areas provided by the introduction of the additional materials 111 into the thermal zone.

The present invention also contemplates, in another embodiment, that such additional materials 111 could be used without heat conductive material 100. Additional materials 111 as described herein also conduct geothermal heat from rock surrounding the thermal zone to the heat exchanging element 104.

The present invention also contemplates that the system may further include the equilibrium temperature being increased by increasing the surface area of the rock surrounding the thermal zone; at least one additional bore hole being drilled into the rock to increase the surface area of the rock; and at least one additional material being injected into the thermal zone, wherein the at least one additional material is a heat rod.

Referring now to FIGS. 3A and 3B, showing another embodiment of the present invention in which an inner pipe 205 for conveying a liquid heat conducting material 206 is placed within an outer pipe 203 for conveying a gas 204. The liquid heat conducting material 206 leaves the inner pipe 205 through a gap 212 and is converted to gas 204 in the heat exchanger 211. The gas 204 exits through the area between the inner pipe 205 and outer pipe 203. Outer pipe 203 is thermodynamically coupled to the heat exchanging element 211. Outer pipe 203 draws the heated contents from the heat exchanging element 211 and brings the heated contents upward from the downhole well casing 201 to the surface. The area between the well casing 201 and the outer pipe 203 may be completely insulated 202 to prevent heat loss. By inserting inner pipe 205 inside outer pipe 203, the entire system is self-contained within the well casing 201, and, therefore, forms a closed loop that separates the contents from the environment creating a completely environmentally-friendly system. The system and materials used in this embodiment are otherwise consistent with, or substantially similar to, those used in the embodiment described above.

Referring now to FIG. 4 which graphically depicts a well 210 in which the system of the present invention may be utilized. The well casing 201 has positioned therein an inner pipe 205 nested within an outer pipe 203. The space between the well casing 201 and the outer pipe 203 is filled with an insulating liquid medium 202. The liquid heat conducting material 206 flows into and down through the inner pipe 205. Inner pipe 205 may be fitted with a one-way valve 207 so that the liquid heat conducting material 206 does not reverse direction and flow back towards the heat exchanger 502. Liquid heat conducting material 206 at the bottom of the inner pipe 205 approaches, and then enters into, the heat exchanger 211. The insulating medium 202 absorbs and retains geothermal heat through the well casing 201. Liquid heat conducting material 206 at the bottom of inner pipe 205 exits 209 through the heat exchanger 211 and transitions from liquid phase to gas phase. The gas 204 rises upward through the space between the outer pipe 203 and the inner pipe 205.

As explained earlier herein, this heat conductive material 206 expands during the liquid gas phase change which causes increased pressure on the system which may cause back pressure on the liquid heat conductive material inside inner pipe 205. The one way valve 207 prevents this pressure from causing the material to flow upwards towards the surface. Because the pressure difference between phases is know or can be ascertained for the heat conductive materials used in the present invention, the hydrostatic pressure gradient exerted at the bottom of the well 209 can be calculated based on the cross-sectional volume and height of inner pipe 205. Once the heat conductive material 206 has been inserted into the inner pipe 205, it will begin to heat up until it becomes fully heated, ultimately reaching it gas-vapor transition point within the heat exchanger 211.

In some embodiments, the area outside of the outer pipe 205 is filled with insulation 202 that keeps the heated contents hot as it travels up the inside of the outer pipe 205. This minimizes energy loss so the contents can be used more efficiently for the generation of power at the top of the well. In addition, or alternatively, the insulation may possess specific heat transfer characteristics that, for example, draw heat away from the well casing 201 and towards the outer pipe 203. In some embodiments, the insulation 202 may be configured to facilitate the flow of heat through the well casing and towards the outer pipe in and around the heat exchange zone, and configured to impede the flow of heat away from the outer pipe in other areas to maintain a temperature of the contents of the piping system substantially constant as the contents of the piping system are pumped to the surface of the well. It may be desirable, for instance, to configure insulation within the well casing such that it facilitates the flow of heat through the well casing and towards the outer pipe around the heat exchange zone and along the pipe while the temperature of the gas inside the outer pipe is greater than 200° F. and then configure the insulation from that point to the surface with an insulation that impedes the flow of heat away from the outer pipe to maintain the temperature of the gas at or above 200° F.

One example of a material with heat transfer characteristics that may be desirable in certain embodiments of the present invention is sold by PocoGraphite, Inc. under the trademark PocoFoam. PocoFoam is an open cell foam with a thermal conductivity up to ten times greater than metallic foal materials, with an in-plane thermal conductivity of 26 BTU*ft/ft²*hr*° F. and an out-of-plane thermal conductivity of 78 BTU*ft/ft²*hr*° F.

It is to be understood that the geothermal temperature may differ within each well and for different contents depending on a variety of factors. For example, the type of rock present within a well may be a factor in determining the depth, size, and materials used in constructing a thermal zone and the type and quality of the heat conductive material 206. The surface area of the rock within the well influences the heat conductivity of the rock, yielding different ranges of temperatures for the equilibrium temperature. The equilibrium temperature may therefore be a range of temperatures and may vary according to the heat needed to be obtained to heat the contents to a desired point.

Referring now to FIG. 5 which graphically depicts a horizontal well 210 of a similar configuration to that shown in FIG. 4. The end 212 of the well 210 may extend well over 1,000 feet into the earth. The curved well casing 201 has positioned therein an inner pipe 205 nested within an outer pipe 203, and both inner pipe 205 and outer pipe 203 are configured to align with curved well casing 201. Once again, in some embodiments, the space between the well casing 201 and the outer pipe 201 is filled with an insulating liquid medium 202. The liquid heat conducting material 206 flows into and down through the inner pipe 205, approaches, and then enters into, the heat exchanger 211, transitions from liquid phase to gas phase, and rises upward through the space between the outer pipe 203 and the inner pipe 205.

As shown in FIG. 4 and FIG. 5, hot gas 204 exit is the top of the well 210 and enters a first heat exchanger 502 wherein the hot gas 204 is cooled. Heat from the heat exchanger 502 is passed through line 503 to a suitable work-expansion device 504. Device 504 may be a turbine, but it also may be any other form of engine that operates by expansion of the vaporized heat-exchange medium. Rotation of a turbine 504 can be used to drive an electrical generator 506 to generate electricity 508.

The gas 504, now changed into a liquid phase after passage through heat exchanger 502, may optionally be further cooled by passage through a second heat exchanger 510 before being deposited in a liquid reservoir 512 for storage. The desirability of using heat exchanger 510 will depend on, among other things, the depth of the well 210 and the type of heat-exchange medium. With the teaching of this description, the flow rate of the heat-exchange medium, and sizing of the equipment can be determined by those skilled in the art. As necessary, liquid from the reservoir may be pumped by a pumping system into inner pipe 205 to reinitiate the process.

Referring now to FIG. 6, and with further reference back to FIG. 5, wherein a flow-chart describes steps in a process for extracting geothermal heat and generating electricity utilizing the system and method of the present invention. A well is drilled and cased via bore well casing 201, and the surface area of the rock at a desired depth may be increased in step 300. The desired depth is determined as a function of the desired temperature to which the contents of the inner pipe 205 and the outer pipe 203 are to be heated, based on the type and surface area of the surrounding rock.

An outer pipe 203 is inserted into well casing 201, 310. In some embodiments, the area between the well casing 201 and the outer pipe 203 is filled with insulation 202 as shown in step 320. The insulation 202 helps to keep the heated contents hot as it travels from the bottom of the well 212 upward, thereby minimizing energy loss so the heat can be used for the generation of power.

The inner pipe 205 can then be inserted into the outer pipe 203 leaving a gap or opening between the distal end of the inner pipe 205 and the distal end of the outer pipe 203. The area of the gap or opening creates a heat exchanges element with sufficient heat to convert the heat conductive material 206 from its liquid phase to its gaseous phase. It's important to note that, although heat exchanger 211 is identified in many embodiments herein is not a separate apparatus or device, it typically refers to a region or a zone in which there is sufficient heat to cause the heat conductive material 206 to change from its liquid phase to its gas phase and that it does not refer to the addition of another device or apparatus other than the configuration of the inner pipe 205 and the outer pipe 203 as described herein. Also, in many embodiments the inner pipe 205 and outer pipe 203 are treated and cleaned coiled tubing so that the heat conductive material 206 in liquid form passing through the inside of the inner coiled tube 205 and the gas form 202 passing between the inside of the outer coiled tube and the outside of the inner coiled tube form a closed-loop system, thereby eliminating the possibility of contamination by contact with contaminants outside the outer coiled tube.

As discussed previously, coiled tube may be used because it has no joints to leak or fail, the total length can be clean treated as a single unit, it can be less expensive than other options and it is reusable. However, practice of the present invention is not limited to the use of coiled tubing and, depending on the specific circumstances of the application, other forms of tubing or pipe are also well suited for use in the present invention.

Once the inner pipe 205 and outer pipe 203 have been installed in the well 210, the inner pipe 205 is completely filled with the heat conductive material 206 from the bottom up 350. This is accomplished by injecting the heat conductive material 206 into the well 210 via inner pipe 205. In an alternate embodiment, a one-way valve 207 is positioned within inner pipe 205 to prevent the heat conductive material from flowing out through the top of the well 210.

Once the inner pipe 205 has been completely filled with heat conductive material 206, the heat conductive material 206 will begin to increase in temperature until an equilibrium temperature is reached, thereby conducting geothermal heat from the hot rock surrounding the thermal zone at the bottom 209 of the well 210 to the heat exchanging element. Once the heat conductive material 206 reaches the equilibrium temperature, the material may be pumped through the heat exchanger 211 as in step 360 causing the temperature of the material to increase to a point at which it undergoes a phase transition to a gaseous phase 205 as it exits the bottom of the inner pipe 205 and enters the bottom of the outer pipe 203. Hence, the heat conducting material 206 forms the contents of the inner pipe 205 in liquid form and the outer pipe 203 in gaseous form to form a closed-loop, solid state heat extraction system.

The gas 204 then flows out of the well 210 and into the electricity generating component and the thermal engine at the surface, where the heat from the contents is used to generate electricity as in step 370 utilizing techniques well known in the art.

In an alternative embodiment, as discussed above, the system may include multiple, additional materials used in conjunction with the heat conductive material 206. In this embodiment, the system may include several holes which have been drilled into rock surrounding the thermal zone to increase surface area by filling the several holes with the additional materials. Geothermal heat flows from the cracks and crevices formed in the rock by drilling the several holes. Certain embodiments of the present invention contemplate that, prior to placing inner pipe 205 or outer pipe 203 in the well casing 201, the surface area of the rock may be increased as much as possible to maximize the flow of geothermal heat from the surrounding rock and into the heat exchanging element 211 via the heat conductive material 206. Use of additional materials also allows more of the fluid to be heated to a desired temperature and therefore more electricity to be generated.

In another embodiment, heat exchanger 211 may include multiple, additional heat exchanging components and/or heat exchanging elements with many different configurations of internal components. Increasing the time that the heat conductive material 206 is inside inner pipe 205 and outer pipe 203 and heat exchanger 211 increases the amount of fluid or gas that can heated inside the thermal zone. One such configuration is a helix formation in which the internal components are a series of intertwined pipes. Other configurations such as twisted pipes exemplify the embodiment in which increasing the length of pipe (and, therefore, the distance contents must travel within heat exchanger 211) increases the amount of contents that can be heated.

While the present system and method has been disclosed according to the preferred embodiment of the invention, those of ordinary skill in the art will understand that other embodiments have also been enabled. Even though the foregoing discussion has focused on particular embodiments, it is understood that other configurations are contemplated. In particular, even though the expressions “in one embodiment” or “in another embodiment” are used herein, these phrases are meant to generally reference embodiment possibilities and are not intended to limit the invention to those particular embodiment configurations. These terms may reference the same or different embodiments, and unless indicated otherwise, are combinable into aggregate embodiments. The terms “a”, “an” and “the” mean “one or more” unless expressly specified otherwise. The term “connected” means “communicatively connected” unless otherwise defined.

When a single embodiment is described herein, it will be readily apparent that more than one embodiment may be used in place of a single embodiment. Similarly, where more than one embodiment is described herein, it will be readily apparent that a single embodiment may be substituted for that one device.

In light of the wide variety of downhole heat exchangers known in the art, the detailed embodiments are intended to be illustrative only and should not be taken as limiting the scope of the invention. Rather, what is claimed as the invention is all such modifications as may come within the spirit and scope of the following claims and equivalents thereto.

None of the description in this specification should be read as implying that any particular element, step or function is an essential element which must be included in the claim scope. The scope of the patented subject matter is defined only by the allowed claims and their equivalents. Unless explicitly recited, other aspects of the present invention as described in this specification do not limit the scope of the claims. 

1. A system for extracting geothermal heat from within a bore hole, comprising: well casing extending downward from the surface of the earth; an outer pipe positioned concentrically within the well casing and extending downward into the well casing, wherein the lower end of the outer pipe is configured with an end to prevent the passage of water therefrom; an inner pipe positioned concentrically within the outer pipe and extending downward into the outer pipe, wherein the lower end of the inner pipe is proximal to the lower end of the outer pipe; a fluid delivery system for delivering fluid into the upper end of the inner pipe; a gas recovery system for recovering gas from the upper end of the outer pipe and converting the gas to work.
 2. The heat extraction system of claim 1, wherein the fluid passes downward through the inner pipe and exits the bottom of the inner pipe and is prevented from entering the well casing due to the end of the outer pipe, geothermal heat sufficiently heats the water to cause a phase change from liquid to gas, and the gas rises through the space between the outside of the inner pipe and the inside of the outer pipe.
 3. The heat extraction system of claim 1, wherein at least a portion of the outer pipe and the inner pipe extend horizontally under the surface of the earth.
 4. The heat extraction system of claim 1, wherein the well casing include cracks or crevices in the rock resulting from the drilling of the well casing.
 5. The heat extraction system of claim 1, further including insulation placed between the outside of the outer tube and the inside of the well casing.
 6. The heat extraction system of claim 1, further including insulation placed between the outside of the outer tube and the inside of the well casing, wherein the insulation is configured to retain heat within the outer pipe in areas proximal to the surface of the earth and facilitate the flow of heat towards the outer pipe in areas proximal to the lowest end of the outer pipe.
 7. The heat extraction system of claim 1, further including a one-way valve inside the inner pipe, thereby preventing the fluid from reversing flow towards the surface of the earth.
 8. The heat extraction system of claim 1, wherein the conversion of gas to work includes the generation of electricity.
 9. A method for extracting geothermal heat from within a well casing, comprising: extending a well casing downward from the surface of the earth; extending an outer pipe downward into the well casing, wherein the outer pipe is arranged concentrically within the well casing and wherein the lower end of the outer pipe is configured with an end to prevent the passage of water therefrom; extending an inner pipe downward into the outer pipe, wherein the inner pipe is configured concentrically within the outer pipe and wherein the lower end of the inner pipe is proximal to the lower end of the outer pipe; delivering a fluid into the upper end of the inner pipe; recovering gas from the upper end of the outer pipe and converting the gas to work.
 10. The method of claim 9, wherein the fluid passes downward through the inner pipe and exits the bottom of the inner pipe and is prevented from entering the well casing due to the end of the outer pipe, geothermal heat sufficiently heats the water to cause a phase change from liquid to gas, and the gas rises through the space between the outside of the inner pipe and the inside of the outer pipe.
 11. The method of claim 9, wherein at least a portion of the outer pipe and the inner pipe extend horizontally under the surface of the earth.
 12. The method of claim 9, wherein a bore hole around the well casing includes cracks or crevices in the rock resulting from the insertion of the well casing in the bore hole.
 13. The method of claim 9, further including insulation placed between the outside of the outer tube and the inside of the well casing.
 14. The method of claim 9, further including insulation placed between the outside of the outer tube and the inside of the well casing, wherein the insulation is configured to retain heat within the outer pipe in areas proximal to the surface of the earth and facilitate the flow of heat towards the outer pipe in areas proximal to the lowest end of the outer pipe.
 15. The method of claim 9, further including a one-way valve inside the inner pipe, thereby preventing the fluid from reversing flow towards the surface of the earth.
 16. The method of claim 9, wherein the conversion of gas to work includes the generation of electricity. 